Freshwater jellyfish surprise swimmers and boaters in Ontario lakes

Sightings of the small, umbrella-shaped creatures, an invasive species, aren’t as rare as you might think.

Graham Chivers and Tracy Munson found this freshwater jellyfish while fishing on Belmont Lake, about 60 km north of Trenton. Dozens of sightings of the invasive species, Craspedecusta sowebyi, have been reported in recent years in Ontario and beyond.

By:Alex BallingallStaff Reporter, Published on Tue Sep 18 2012

They’re down there, beneath the surface, pulsating gently like so many translucent hearts. Only they have tentacles. And toxic barbs.

Freshwater jellyfish — forms of hydrozoa called Craspedacusta sowerbyi — are surprising swimmers and fishers in lakes and rivers across Ontario and beyond.

“I have several hundred reports from 2012” alone, says Terry Peard, a retired biology professor in Harrisburg, Pa., who keeps tabs on sightings of the quarter-sized invertebrates on his website, freshwaterjellyfish.org.

“I’m getting so many (reports) every day, by the time I respond to all of them, the day’s gone.”

His site lists dozens of reported sightings from across Canada, mostly in Ontario, B.C., and Quebec, as well as encounters throughout the U.S. and around the world. He says freshwater jellyfish aren’t as rare as you might think. The undulating invertebrate can be found on every continent except Antarctica.

On Monday, 43-year-old Graham Chivers was fishing with his girlfriend on Munn Bay in Belmont Lake, about 60 km north of Trenton. They caught a pike and were about to pack it in when they noticed a “tiny blotch” next to the boat. To their surprise, it was a jellyfish.

“I grabbed my bail bucket and scooped it up,” says Chivers, who spotted about 50 more as he drifted in his boat.

Michelle Wolfson, a Toronto mother and avid sailor, has twice come across clusters of the squishy creatures, once in 2010 in the Bay of Quinte, and again in Go Home Lake near Georgian Bay.

“People don’t believe you at first,” she says. “There were hundreds of them.”

The small, umbrella-shaped jellyfish is an invasive species thought to have originated in China’s Yangtze River, says Peard. They were first documented in the late 19th century, and are thought to have spread from China attached to plants and the bottoms of boats.

Because they are typically found drifting in warm water, global warming is often cited as an explanation for the seeming spike in sightings.

But Peard thinks the Internet is also helping people more easily identify them, and report their encounters. “I think it’s a combination,” he says.

Freshwater jellyfish feed on whatever small food they get their tentacles on — mostly plankton, insect larvae and small worms, Peard says. They use toxic barbs on the ends of their tentacles, which protrude from the rim of their round bodies, to sting and pull in prey.

And no, they’re not harmful to humans.

“I don’t think it can penetrate human skin,” he says, citing more than 20 years of experience studying the creatures at the Indiana University of Pennsylvania. “We’ve handled them bare-handed for years, and we’ve never felt anything.”

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